In the prior art, an Internet Protocol version 6 (fully spelled as Internet Protocol version 6 in English, and referred to as IPv6 for short in English) multicast address constructed by using an Internet Protocol version 4 (fully spelled as Internet Protocol version 4 in English, and referred to as IPv4 in English) multicast address may be used as a destination address of a unidirectional multicast data stream in an IPv4-in-IPv6 encapsulation mode, and an IPv6 address of a multicast source may be constructed by using an IPv4 unicast address of the multicast source according to a format defined in RFC6052, so that a multicast Basic Bridging BroadBand (fully spelled as Multicast Basic Bridging BroadBand in English, and referred to as mB4 for short in English) device or a customer premise equipment (fully spelled as Customer Premise Equipment in English, and referred to as CPE for short in English) in an access network can receive a multicast packet in a network in which an IPv4 node and an IPv6 node are located. The mB4 device is responsible for decapsulating a received IPv4-in-IPv6 multicast packet, and forwarding an IPv4 multicast data stream to an IPv4 receiver, for example, a set-top box (fully spelled as Set Top Box in English, and referred to as STB for short in English).
In addition, a multicast address translation router is a node in a dual-stack network and processes a Protocol Independent Multicast (fully spelled as Protocol Independent Multicast in English, and referred to as PIM for short in English) join request packet, a Multicast Listener Discovery (fully spelled as Multicast Listener Discover in English, and referred to as MLD for short) join request packet, or an Internet Group Management Protocol (fully spelled as Internet Group Management Protocol in English, and referred to as IGMP for short in English) join request packet. For example, the multicast address translation router checks whether a joining IPv6 multicast address belongs to a certain mPrefix64 (prefix information of IPv6), that is, checks whether it is an IPv4 multicast address in an IPv4-in-IPv6 encapsulation mode; moreover, the multicast address translation router is responsible for copying an IPv4 multicast data stream to an IPv6 domain, and sending the IPv4 multicast data stream in an IPv6 network in the IPv4-in-IPv6 encapsulation mode.
Generally, for the objectives of reliability and load balancing, several nodes (for example, an IPv4 node or an IPv6 node) in a network may be embedded with a function of the multicast address translation router. In this case, each multicast address translation router creates an IPv4-in-IPv6 multicast packet by using a same multicast prefix mapping rule and unicast prefix mapping rule.
In a dual-stack network, the multicast address translation router belongs to an IPv4 multicast distribution tree; however, a path from the multicast address translation router to an IPv4 source is not necessarily on a reverse shortest path distribution tree of the source. As a result, a multicast distribution tree path selected in the prior art may not be an optimal multicast distribution path, causing low efficiency of multicast stream transmission and transmission delay.